1999 Toyota 4Runner P 0171 "Engine running too lean&qu

Tiny
SARARADKA
  • MEMBER
  • 1999 TOYOTA 4RUNNER
Engine Performance problem
1999 Toyota 4Runner 6 cyl Four Wheel Drive Automatic 140K miles

I have been getting the code P 0171, "Engine running too lean" on my 1999 Toyota 4Runner (3.4, 6 cyl.) Over the past year.
When the light first came on, I replace both O2 sensors. The light stayed off for about a month.
I then took it to a shop, and had vacuum lines reconnected, the spark plugs and wires replaced, and had diagnostics done. The mechanic told me that the 4Runner was throwing all kinds of fuel at the engine, but it wasn't making through the system properly. That makes sense, because my exhaust smells rich, but there is reduced power and gas mileage. The mechanic was unable to fix the problem.
After spending my available repair funds at the shop, and still having a check engine light on, I did more research, bought some MAF sensor cleaner, cleaned the MAF sensor, and the light went off, and the car ran fine.
The light came back on a month later.
I then replaced the MAF sensor all together. No change.
It has started idling low enough to stall, and is hesitating to start randomly.
Air filter and fuel filter have also been replaced in the last 6 months.
Any ideas?
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Monday, June 29th, 2009 AT 9:17 AM

3 Replies

Tiny
DOCFIXIT
  • EXPERT
Hi
Has fuel pressure been checked should be 38-44 psi?
Also was a scan check done on Camshaft sensor?
Let me know
Thanks for donate
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Monday, June 29th, 2009 AT 10:56 AM
Tiny
BEKUHN
  • MEMBER
I feel your frustraton! FYI, I have a mech friend with the diagnostic device that reads these codes. Brought my 2000 4Runner to him with the same P0171. We were able to reset my light. Suspect the cause of my problem was the engine air filter box; the cover had popped ajar at some point (which was likely causing too lean a fuel/air mixture).

Important part is this; I was able to sit with him as the computer read, page by page, through the codes and diagnostics. If nothing else, I gained peace of mind as each page of diagnostics showed the engine performance to be "OK", to include 'pending' problems. All this was done in a matter of minutes (ever wonder how long most mechs ACTUALLY devote to your vehicle in most cases!). If you have a trustworthy mech, I'd recommend asking him if he'll allow you to review the diagnosis with him, and have him tell you page by page what's good with the car (and what's not). Otherwise, you'll remain in the shroud of mystery every time the light comes back-- and pay them a hefty some on EACH return (like so many before you). Hmmm. Get it!

Lastly, the diagnostic device (known sometimes as an OBD2) costs as low as $65, is 'plug & play', and is universal for any auto. If you're reading this email, you probably have enough 'tech-savvy' to operate it. Keep this in mind on your next trip back to your mech for the same repeat gripe!
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Monday, June 29th, 2009 AT 11:44 AM
Tiny
SARARADKA
  • MEMBER
Thanks for the response, guys. I will be looking into purchasing my own diagnostic device.
My father suggested that this problem might be caused by a bad/worn-out/gunked-up fuel filter. Since that wasn't ever mentioned in my manual, or any internet research that I did, it makes me wonder, but the relation to fuel pressure makes it viable.
Has anyone come across a bad fuel pump as a cause for a P0171 error code?
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Monday, June 29th, 2009 AT 2:43 PM

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